This CL replaces most of Isolate::GetEnteredContext with
GetEnteredOrMicrotaskContext, as it should be more relevant.

Here is a brief overview of the series of changes.
https://docs.google.com/document/d/1MY_xlsYS7E6_qbwwY66-FH3JkAYeTHBlF5qVBrBpWyY/edit#heading=h.fx2rezbyzz5c

Bug: v8:8124
Change-Id: I27355e325a92094240c25b672d1219f3214a9da0
Reviewed-on: https://chromium-review.googlesource.com/c/1297654Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57470}